In a signal transmitting and receiving system configured to have a transmitter and a receiver connected to each other via a transmission path, a data array sent from the transmitter arrives at the receiver via the transmission path and is received by the receiver. In many signal transmitting and receiving systems, the transmitter converts parallel data into serial data and sends the serial data to the transmission path, and the receiver receives serial data and converts the serial data into parallel data.
The signal waveform of a data array when it arrives at the receiver is deteriorated compared to the signal waveform of the data array when it is sent from the transmitter. This deterioration in signal waveform is caused due to the frequency characteristics of the transmission path attenuating a high-frequency component more than a low-frequency component. When the degree of deterioration in signal waveform is significant, the frequency of erroneous receiving (bit error rate) of the receiver increases. Therefore, in many cases, receivers include an equalizer in the preceding stage of a sampler.
Since an equalizer has frequency characteristics capable of improving the frequency characteristics of a data array which has arrived from the transmitter, a deteriorated signal waveform can be restored, or the degree of deterioration can be reduced. Generally, since transmission paths attenuate a high-frequency component, the equalizer increases a high-frequency component of a data array or decreases a low-frequency component of the data array to improve the frequency characteristics of the data array. The sampler inputs the data array adjusted by the equalizer and outputs a logical value according to the result of magnitude comparison between a voltage value of a bit and a reference value for each bit of the data array. Equalizers of various types have become known. Examples of representative equalizers include continuous time linear equalizers (CTLEs) and decision feedback equalizers (DFEs).
The frequency characteristics of an equalizer ought to be set to compensate for the frequency characteristics of a transmission path between a transmitter and a receiver. In addition, since transmission paths vary in material and shape and vary in transmission characteristics, it is important to appropriately set an equalizer in an actual signal transmitting and receiving system configured to have a transmitter and a receiver connected to each other via a transmission path. Various algorithms for adjusting the frequency characteristics of an equalizer have become known, and examples of representative algorithms include sign-sign least mean square (SSLMS) (refer to Non-Patent Literature 1).
[Non-Patent Literature 1] V. Stojanovic, et al., “Autonomous Dual-mode (PAM 2/4) Serial Link Transceiver with Adaptive Equalization and Data Recovery”, IEEE JSSC, vol. 40, no. 4, pp. 1012-1026, Apr. 2005